The present invention is directed to a combination of a gripper bar and a device for fastening the gripper bar at each end onto a chain train in a machine that processes plate-like workpieces, such as sheets of cardboard or sheets of paperboard.
A machine for processing sheet-like workpieces usually includes an infeed station in which a pile of the sheets is arranged, with every sheet being successively taken from the top of the pile in order to be carried onto a feeding table. On the feeding table, every sheet is positioned against front lays and side-marks before a front edge of the sheet is seized by a series of grippers fitted along a crosswise bar, whose ends are fastened into a train of lateral continuous chains which carry the bar and also the sheet into the next processing stations. The processing stations can include a die-cutting press, which is usually followed by a waste stripping station. These processing stations are followed by a delivery station in which every sheet is released by the grippers and is aligned prior to being dropped on top of an outlet pile.
The device for fastening the gripper bars onto the two trains of lateral continuous chains, which chains form a loop that passes around a driving chain wheel and a driven chain wheel, has to be very solid in order to transmit to the bars and, hence, to the sheet, the acceleration and deceleration forces which appear in the course of an intermittent run at high speed throughout the successive stations. Moreover, the crosswise bars, which support the grippers, are usually made out of rather complex profiled pieces in order to remain rigid to flexing and bending, which fact complicates the construction of the fastening device even more.
Moreover, the fastening device must allow a certain slack, i.e., a limited movement of the bar with regard to the chain trains in the sheet travelling direction so as to permit, by complementary means, an ultimate adjustment of the position of the sheet independent from the chain standstill position in a processing station. On the other hand, this fastening device is to remain rigid to rotation around the axle, which passes by the chain in order to limit, as much as possible, the flexing of the bar due to the centrifugal forces occurring during the movement of the chains and, particularly, when the chains pass around the driving and driven chain wheels arranged, respectively, at the beginning and the ending of the course of travel through the machine.
The known fastening devices usually include a first so-called fixed part, which is an integral part of the chain and is to replace a link, and a second so-called slack part, which is connected to the bar and slides in or on the first part of the fastening device in the sheet travelling direction against the effect of the elastic means, such as a spring. Moreover, one of the parts includes a finger extending parallel to the bar and sliding crosswise in the other part and this finger insures a rigidity of the fixture during the flexing of the bar in the course of the bar passing around the driving and driven chain wheels.
However, the respect given to the above-mentioned characteristics implies that the constitutive pieces of the actual devices be of a complex construction and therewith expensive. Moreover, the known fastening devices are different, depending whether they are designed for the left-hand side chain, which is the operator's side, or the right-hand side chain, which is opposite the operator's side, which fact compels the maintenance of a double stock of repair parts which are substantially symmetrical. In addition, the conception of the actual fastening device makes it impossible to dismantle the gripping bar for fixing or replacement without having to open the chain trains, which process of opening the chain trains is particularly difficult and fastidious operation. Finally, due to the complexity of these fastening devices, the areas for the ultimate position of adjustments are often located under the lower side, which fact, in the course of such adjustments, develops a clockwise rotational torque that tends to make the gripper look or rotate downward.